1. Field of the Invention
The present invention relates to a wireless local loop system, and more particularly, to an integrated wireless local loop terminal.
2. Background of the Related Art
In general, the wireless local loop (hereafter called as ‘WLL’) system provides a wireless subscriber line to connect between a local switching center and home or office, not by wire, but by radio telecommunication, for providing voice, facsimile, and data communication services.
The WLL is called as RITL (Radio In the Loop), FRA (Fixed Radio Access), FWA (Fixed Wireless Access), or FCS (Fixed Cellular System) in some countries, and is one of technical fields that draws attention of communication providers. The WLL system has been devised by AT&T Bell Laboratory in early 1970 for a sparsely populated region, such as fishing and agrarian villages, for reducing installation cost.
However, because securing radio frequencies was not easy, and costs for manufacturing and installation of antennas and radio transmitters/receivers were excessive, the WLL system could not be put into practical use. However, as semiconductor and electronic communication technologies are developed rapidly in 1990s, the problems, such as frequency efficiency, radio channel quality, and installation cost per subscriber, are solved so that many manufacturers can now produce economical products.
The communication providers pay attention to the WLL system because of the following features of the WLL system.
First, installation of subscriber lines is easier than a current subscriber line network in which the connection from a local switchboard to a subscriber home is made by a line. Also, an installation time period required until starting of service is reduced.
Second, the WLL system has a merit in view of endurance of service because the WLL system can be used as an emergency subscriber line in case of damage to the current subscriber line network caused by natural disaster, or the like.
Third, the WLL system can provide flexible services with respect to a variety of service requirements, such as POTS (Plain Old Telephone Service), data service, and ISDN.
Fourth, installation cost is fixed regardless of distance, such that an initial investment cost is reduced, and recuperation of the investment is faster.
Fifth, a WLL system network can be expanded quickly corresponding to an increased subscriber demand.
The WLL having the foregoing features is considered to be the most potent method for construction of a subscriber network quickly by a telephone service provider, or a communication service provider, and further considered as a fundamental communication structure of a developing country that has a POTS.
In the meantime, although the WLL is similar to a mobile communication network in view that radio channels are used as communication media, the WLL has an advantage in that the WLL has an electronic wave environment substantially robust than the electronic wave environment of the mobile communication network because the WLL has no mobility. Besides, the WLL had the following features in comparison to the mobile communication network.
Although the environment of the mobile communication network has a wave path loss in a range of 40 dB/decade because the environment is a non-line-of-sight environment because of blocking, reflection, and refraction of a straight wave by surrounding buildings as the antenna is located at a place lower than the surrounding buildings, the environment of the WLL has a wave path loss as low as 20 dB/decade because the environment is a line-of-sight environment because the antenna is located at a rooftop and a mobility of the antenna is limited, permitting to serve a larger area by using the same power.
Because the electronic wave environment of the WLL is a stationary communication of a point to point type, the electronic wave environment of the WLL has substantially less fading caused by multiple paths than the electronic wave environment of a mobile communication network that has a point to mobile station type.
The WLL requires no hand-over as the WLL is a stationary radio communication network. Therefore, the WLL requires no reserved radio channels for the hand-off that is required in the mobile communication network. These reserved radio channels may be used for general calls permitting to obtain effects of an increased radio channel efficiency and an increased subscriber capacity. The radio link between a building and a base station can be constructed in a direction for reducing interference to a particular subscriber, and because there is no change of the radio link unless the subscribers are substantially increased or a cell is divided, a design of the WLL is substantially simpler than a mobile communication network.
Moreover, the stationary radio communication of the WLL permits the use of directional antenna on forward/backward links for reducing an identical channel interference to respective subscribers, that in turn permits to reduce a distance of frequency re-use. The reduction of frequency re-use distance brings about an increased subscriber capacity per unit area.
Basically, the WLL is provided with a telephone set, an NIU (Network Interface Unit) that makes a wireless communication between the telephone set and a local switching center possible, a base station, a base station controller, a base station managing device, and the like.
The NIU is located at the final stage of network elements for carrying out functions of transmission/reception of a radio signal, modulation/demodulation of a radio channel, voice compression/decompression, and access to a PSTN terminal. There may be various forms of terminals depending on applied technologies. For example, a terminal with built-in RF function, a terminal with separate RF function and a handset, and the like, and a single line, or multiple line may be provided.
The base station is located between the NIU and the base station controller, and connected to the NWJ by radio signal, and to the base station controller by line, for transmission/reception of a radio signal, power control, modulation/demodulation of a channel, protocol transform for signal transmission/reception with the NIU and the base station controller. The base station is provided with an antenna transmitter/receiver, a power amplifier, channel cards, and hardware for interface with the base station controller.
In making a radio access with the NTU, the base station has a limitation of a capable cell radius caused by limitations in the electronic wave environment and a radio power, to require the base station controller for effective access to a wireless section and a wired section. The base station controller is located between the local switching center and the base station for connecting the local switching center and the base station and managing the base station. The base station controller is connected to respective base stations by wire mostly, and for managing radio resources, transcoding, base station managing, and a function of base station and switchboard match.
The base station managing device performs managing and maintenance of entire equipments in the WLL, such as network system managing, performance managing, data processing, software management, security management, and the like.
The telephone set and the NIU correspond to a WLL terminal of the present invention. There are a separate type WLL terminal and one piece type WLL terminal in the foregoing WLL terminal depending on connection between the telephone set and the NIU.
That is, the separate type or modular type WLL terminal has a stationary telephone set and a separate NIU connected to the terminal by cable and preferably used by wire for purchase of, not the telephone set, but the NIU only, when a subscriber having the stationary telephone set connected to an existing wire network intends to subscribe to the WLL.
The one piece type integrated WLL terminal has a telephone set and the NIU integrated as one unit and preferably used by a subscriber who has no stationary telephone set connected to an existing wire network.
A related art one piece type WLL terminal will be explained. FIG. 1A illustrates an exemplary view of the related art WLL terminal, and FIG. 1B illustrates a block diagram of the related art WLL terminal.
Alike a general wire telephone set, the related art WLL terminal is provided with a body 1 having a telephone unit and the NM built therein, a handset 2 separated from the body 1, and a coil line 3 connected between the handset 2 and the body 1, for transmission/reception of a signal as a hook switch is switched on/off following putting down the handset 2 on the body 1, or holding up the handset 2 from the body 1.
If the user intends to make a call, the user holds up the handset 14 to switch on the hook switch, and dials a telephone number on the key pad 19, for assignment of a channel to the base station, to make a call available by the method explained before. Or the WLL system may be connected to an external instrument (computer, facsimile, or the like) through the data interface part 17 for making communication.
However, the related art WLL terminal has the following problems.
First, since the related art WLL terminal is required to be stationary for receiving power through the AC adapter, the related art WLL terminal is not convenient to use.
Second, transporting of the WLL terminal is difficult, because the WLL terminal has a 2-piece structure of separated handset and body, bulky, and uses a utility power.
Third, in the case of communication with the external instrument (a computer, or a facsimile) through the data interfacing part by connecting the WLL terminal thereto, most of the data interfacing parts have been RS232C (Recommended Standard 232 Revision C) which transmit data in series. However, the RS232C has a slow transmission rate, requires many pins for two transmission and reception lines, five control lines, and one earth line, and needs a separate line driver module for compensating difference of signal levels of a PC signal level and a WLL terminal signal level when the PC is connected to the WLL terminal.